Variable resistor construction



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Sept. 20, 1960 M. E. BouRNs ETAL VARIABLE RESISTOR'CONSTRUCTION OriginalFiled May 5, 1956 United States Patent O VARIABLE RESISTOR CONSTRUCTIONMarlan E. Bourns, Marvin E. Harrison, Donald L. Gaa,

and Richard O. Barrett, Riverside, Calif.; said Harrison, Gaa, andBarrett assignors to Bourns, Inc., a corporation of California Originalapplication May '3, 1956, Ser. No. 582,442.

Divided and this application Mar. 27, 1959, Ser. No. 1

This invention relates to the construction of new and improved variableresistors, and, more particularly, improved potentiometers. Thisapplication is a division of our co-pending application, Serial No.582,422, iiled May 3, 1956, now Patent No. 2,886,881 for VariableResistor Construction.

A number of diierent types of lead screw actuated potentiometers havebeen developed in the past. One particular type of unit of this categorywhich has enjoyed wide commercial acceptance is formed so as to includea base member having an elongated center portion and upstanding ends. Ametal cover is secured about this base portion in this particular unitso as to deline an internal cavity between the two ends and on one sideof the elongated center portion. A shaft is held by these two ends so asto project through this cavity adjacent to an electrical resistanceelement and an electrical return or shorting member. With thisconstruction contact means are mounted upon a movable member carried bythe shaft so as to engage the resistance element and electrical return.

In lowering the cost of potentiometers of the category specificallyindicated in the preceding while simultaneously improving the mechanicalperformance of these units a number of distinct problems have beenencountered. One of these problems concerns the mounting of a resistanceelement in a groove in a quick, cheap, effective manner. One object ofthis invention is to teach the construction of clip members capable ofbeing cheaply manufactured and capable of being easily and convenientlyused so as to securely mount an'electrical resistance element or otherequivalent member within a groove while simultaneously establishingelectrical contact With such an element.

Another object `of this invention is Ato provide a cheap, effecivestructure or construction for mounting and holding la shaft inpotentiometer-s of the category specically indicated in the precedingdiscussion. This latter objective is exceedingly important inasmuch asthe shaft in uni-ts `of the category described must be securely heldagainst -end play, and yet must be mounted in such a manner as toprevent damage :as through too great adjustment of a shaft.

Further objects of this invention as well las many speicic ladvantagesof it will be more fully apparent from the remainder `of thisdescription includi-ng the appended claims 'and the accompanyingdrawings in which:

Fig. l is an isometric view of -a potentiometer of this invention;

Fig. 2 is top view of a potentiometer shown in Fig. 1 with the cover ofthis potentiometer removed;

Fig. 3 is a cross sectional view taken at line 3-3 of Fig. 2;

Fig. 4 is `a sectional view of a complete potentiometer of thisinvention taken at yline 4-4 of Fig. 3;

Fig. 5 is an isometric View of a retaining clip employed with thepotentiometer illustrated in the preceding iigures;

2,953,763 Patented Sept. 20, 1960 ICC Fig. 6 is la isometric view of aspring retainer used with this potentiometer;

Fig. 7 is an isometric view of a spacer for use with this potentiometer;

Fig. 8 is an isometric view of a rubber bushing employed in this unit;

Fig. 9 is a cross sectional view similar to Fig. 3 of a modifiedpotentiometer of this invention;

Fi-g. l0 is a partial view similar to Fig. 2 of the modi- 0 tiedpotentiometer shown in Fig. 9;

Fig. 1l is a cross sectional view taken at line 11--11 of Fig. 9;

Fig. l2 is an isometric view of modified clip used in the potentiometershown in Fig. 9; and

Fig. 13 Vis an isometric view of a modified electrical return used withthis potentiometer.

In yall iigures of the drawing like numerals are used to designate likeparts wherever convenient for purposes of illust-ration and explanation.that this invention is not be considered as being limited topotentiometers lhaving the precise proportional sizes and shapes showninasmuch as the basic principles of this invention can be readilyapplied to a number of other different units with a minimum of diiculty.

I-t may be indica-ted by way of la summary which will help understandingof this invention that it is primarily concerned with potentiometerswhich include: a base member formed of a non-conductive material so asto include an elongated center portion and upstanding ends; a metalcover secured about this base member between the two ends thereof so lasto dene an elongated internal cavity on one side of the elongated centerportion; means for :holding `a shaft formed in the upstanding endsadj-acent to the cover; retainer means located in said means for holdinga shaft in an operative position; a shaft held by said retainer means soas to project through the cavity and out of one end of thepotentiometer; a movable member mounted upon this shaft within thecavity; an electrical resistance element located generally upon thecenter portion of the lbase member; `clip means holding the electricalresistance element in this position `and establishing electricalcommunication with the ends `of this resistance element; an electricalreturn `located upon the center portion of the base member adjacent; tothe electrical resistance element; terminal means leading from the clipmeans and the electrical return to the outside of `the potentiometer solas to connect these elements into 1an electrical circuit; and contactmeans mounted upon the movable member so as to establish electricalcommunication between the resistance element a-nd the electrical return.

The precise nature of the invention is best explained directly byreference to the drawings. Here there is shown a potentiometer 10 havingia base member 12 formed of a nonconductive material such as a phenolicor other resin so as to include an elongated center portion 14 to theends of which there are attached upstanding ends 16 and 18.

Within the center portion 14 there is located a rst groove 20 havinginternal shoulders 22 which are designed to support the ends ofanelongated electrical return 24 of conductive metal having a generallyU-shape. This return 24 may be conveniently snapped into position.Ratchet like extensions 25 on the sides `of it engage the walls of thegroove 20 so as to prevent dislodgment of this return. Also within thecenter portion 14 parallel to the groove 20 there is located a secondgroove 26 of larger internal dimension; the ends of these two grooves 20and 24 :are connected together by short passages 28.

Within the groove 26 there is located a conventional wire woundresistance element 30 or equivalent, the ends It is to be understood ofwhich are held by spring clips 32, the construction of which is bestseen in Fig. 5 of the drawings. The clips 32 are located, as shown, withenlarged ends of the groove 26 so as to be incapable of lateral movementwithin these grooves. Each of these clips is formed of a conductive,resilient metal in a general U-shape so as to have semicylindricalprojections 34 on the ends thereof facing one another. The ends of theseclips adjacent to the projections 34 are also curved slightly so as tobend towards one another. Upon the sides of the two clips there projectoutwardly small ratchet like extensions 36, and from the bottom of thecenter portion of these clips there project towards the ends of theclips 32 resilient tongues 38 having bent over ends and which areprovided with projections 40 similar to the projections 34. These clipsare `designed in such a manner that the resistance element 30 may bedisposed with respect to them and firmly held in position within thegroove 26 and with a minimum of difficulty. The projections 34 aredesigned to engage the sides of the resistance elements 30 establishingelectrical communication or contact therewith and resiliently holdingthe resistance element in a manner in which it cannot be damaged byvibration. The extensions 36 act as ratchets against the sides of thegroove 26 when the clips 32 are in position preventing accidentaldislodgement of the resistance element 30. The tongues 38 bear againstthe ends and the top of the resistance element 30 so as to resilientlyhold this resistance element in a fixed position in which it cannotslide lengthwise within the groove 26. Electrical wires 42 enter intothe potentiometer through openings 44 in the end 16. One of these wiresis connected directly to the electrical return 24, and the other twowires are connected to` the clips 32 as indicated in the drawing. Thegroove 20 forms a very convenient passage for holding the wires 42 inposition where they cannot interfere with the operation of the completepotentiometer.

Within the top of the end 16 there is formed a generally rectangularcavity 46 which is in connection by means of a groove 49 with anenlarged, elongated cavity 48 formed within the potentiometer 10 when acover 50 of met-al is disposed over the ends 16 and 18 and part of thecenter portion 14. This cover is conveniently held in this location bymeans of metal rivets 52 passing through holes 54 in the ends 16 and 18.Within the other end 18 there is formed la generally rectangular opening56 adjacent to the outside of the potentiometer 10 from which thereleads a groove 58 leading to the cavity 48.

A metal shaft 60 is held so las to project between the ends 16 and 18 sothat a head 62 on the shaft is located against the exterior of thepotentiometer 10. Immediately back of this head the shaft 60 is providedwith a reduced diameter portion 64, the exterior of which is smooth.This portion 64 is adapted to be held by a resilient block 66 of rubberor equivalent material, the construction of which is best seen in Fig. 8of the drawings. Here it is shown that this block has a centercylindrical passage 68 designed to hold the portion 64 and a cut 70which is designed so that the block 66 may be deformed in order tointroduce the portion 64 into the location specified. The block is sodimensioned that it fits tightly around the shaft 60, forming aneffective seal against dirt or the like entering the potentiometer 10.

The other end of the shaft 60 is provided with another portion 72,having a smooth exterior, of reduced diameter which is designed to gothrough the slot 49 so as to extend into the cavity 46. Within thiscavity this portion 72 is provided with two projecting cylindricalflanges 74 which are spaced from one another. These flanges are designedso that a small spring retainer 76 of conductive metal having the shapeshown in Fig. 6 of the drawings may be conveniently located with agenerally U-shaped opening 78 in the center portion of this retainerpositioned over the portion 72 between the flanges 74. Thus, with thisconstruction, portions of the retainer are engaged by the two flanges 74so that the ends 80 of this retainer bear against the wall of the cavity46 pulling or urging the shaft 60 towards the end 16 of thepotentiometer 10. In order for this function to be satisfactorilyachieved, the center portion of this retainer 76 is bowed in much theshape of a common leaf spring. A tab 82 attached to the retainer 76projects from the center portion thereof so as to bear against the cover50, maintaining the retainer 76 and the shaft 60 in the proper position.The tab 82 also serves to place the shaft 60 in electrical communicationwith the cover 50 so as to provide a ground connection for this shaft.

Upon a threaded portion 84 of the shaft 60 there is located anon-conductive movable member 86 which carries resilient spring contacts88, formed of the same piece of metal, designed Ito engage theresist-ance element 30 and the electrical return 24. Because a threadedcylindrical opening 90 within this movable member 86, engaged by thethreaded portion 84 of the shaft 60, must pass over the anges 74 inassembling the potentiometer 10, a bearing spacer 92 is located againstthe flange 74 closest to the end 18 of the potentiometer and against thewall adjacent the groove 49 so as to provide a bearing surface whichprevents movement of the shaft 60 toward the end 18 if the shaft 60 isturned so as to force the movable member 86 against the end 16. Thisbearing spacer 92 is provided with a generally U-shaped opening 94 asindicated in Fig. 7 of the drawings so as to t over the portion 72 ofthe shaft 60, and is so dimensioned as to be held in place by the cover50.

With the preferred embodiment of the invention the movable member 86 andthe spring contacts 88 are so dimensioned that the end of the contact 88engaging the resistance `element 30 so -as to be in electricalcommunication with it is capable of being moved beyond the projections34 on the clips 32 at either end of the potentiometer 10 as indicated bythe positions of these elements in Fig. 2. This is important since theprojections 34 serve as end terminals for the resistance element 30; ithas the result that adjustment can be made over the entire effectivelength of this resistance element, and to a greater extent, that is,beyond the terminals if desired. Being able to provide such adjustmenthas been considered a problem in the past.

In Figs. 9, 10, and l1 there is illustrated a modified potentiometer ofthis invention which is substantially the same as the potentiometer 10except for several differences in the construction of certain parts. Oneof these differences is that the wires 42 are not employed and thatclips 102 (Fig. l2) similar to the clips 32 are utilized in place ofcertain of these wires. All of the parts of the clips 102 which are thesame as corresponding parts of the clips 32 are designated by the primesof the numbers previously employed. With the clips 102 the tongues 38are each formed of a single strip of metal which extends through anopening 104 in the base 12 and which is doubled back on itself so as toextend back through this opening where it terminates in a structure aspreviously described. Small ratchet-like protruding extensions 106formed on each of these metal strips engage the exterior of the `base 12to securely hold each of the clips in position. Further, in thepotentiometer 100 an electrical return 108 (Fig. 13) differing from thereturn 24 is employed. This return is preferably formed out of a singlesheet of metal so as to include a tongue 110 of a single strip of metalbent back along itself having ratchet-like protruding extensions 112formed thereon so that this return can be conveniently snapped intoplace within a smooth walled groove 114 with the tongue extendingthrough an opening 104 and with the extensions 112 engaging the exteriorof the base 12. Similar extension 112 on the sides of an elongatedU-shaped top to the return engage the walls of the groove locking thereturn 108 securely in place.

The structure of the potentiometer 100 so far described s is veryadvantageous since it eliminates the necessity of soldering wires tovarious members and making provision for these wires. Also it is easierto hold the base 12 in this modified device than it is to hold the base12 in the potentiometer 10. The tongues 38 and 110 can be shaped asdesired so as to be capable of being tted into sockets, or so as to becapable of being secured to wires, etc. The assembly of thepotentiometer 100 is also comparatively simple since the clips 102 andthe return 108 can be merely snapped into a permanent position.

In the potentiometer 100 the groove 49 may be replaced by a hole .116through which the portion 72 of the shaft 60' projects. One of the anges74 is omitted with this construction so that a single bowed resilientmetal plate or retainer 118 having an opening formed therein similar tothe opening 78 can be used to hold the shaft 60 in position. The cover50 holds this plate 118 in position. Thus, this part of the constructionof the potentiometer 100 is simpler than the equivalent part of theconstruction of the potentiometer 10.

Those skilled in the art to which this invention pertains will realizethat the constructions defined herein incorporate a number of minorchanges over pre-existing potentiometers of similar category. Whilethese changes are minor, they are nevertheless of major importance froma commercial standpoint inasmuch as they contribute to theconstructionof potentiometers which are eflicient, easy to assemble andwhich can be constructed at a comparatively low cost. These persons willfurther realize that many of the individual features of this inventionhave separate utility apart from the complete invention as a whole,although these features are best employed in conjunction with oneanother. For this reason, certain of these features are separatelyclaimed. It will also be realized that the retainer structure of thepotentiometer 100 can be used with the potentiometer 10, and vice versa;the clip and return structure shown can also be interchanged. Becauseminor changes may be made in the structure shown without departing fromthe essential nature of this invention, the invention itself is to beconsidered as being limited only by the appended claims.

We claim:

1. A variable resistor which includes: a base member ,having anelongated center portion formed of a nonconductive material with agroove formed therein; a cover position upon said base over said groovein said elongated center portion so as to define an internal cavity; anelongated resistance element positioned within said groove; spring clipmeans engaging each end of said resistance element and the walls of saidgroove positioned within grooves at each end of said resistance element,said spring clips means holding said resistance element in place andestablishing electrical termination for said resistance element; a shaftpositioned within said internal cavity; contact means carried by saidshaft so as to engage said resistance element, said contact means beingmovable along said resistance element; and means affording electricalconnections from the outside of said variable resistor attached to saidspring clip means.

2. A variable resistor as defined in claim l wherein said spring clipmeans each is formed of a conductive, resilient metal in a generalU-shape so as to have projections formed on the ends thereof yfacing oneanother and ratchet like extensions projecting outwardly from the sidesthereof, and wherein said projections engage said resistance elements soas to terminate said resistance elements between the ends thereof andwherein said extensions engage the walls of said groove so as to holdsaid clip means in position.

3. A spring clip formed of a conductive resilient metal having agenerally U-shape, said clip including projections on the ends thereoffacing one another, ratchet like extensions projecting outwardly fromthe sides thereof, and a tongue extending from the center thereofgenerally between the sides of said clip toward the ends thereof.

4. A variable resistor which includes: a base member having an elongatedcenter portion formed of non-conductive material with a groove formedtherein; a cover positioned upon said base over said groove in saidelongated center portion so as to define an internal cavity; meansdefining openings in said base member leading from the ends of saidgroove to the exterior of said variable resistor; an elongatedresistance element positioned within said groove; spring clip meansengaging each end of said resistance element and the walls of saidgroove positioned within said groove at each end of said resistanceelement, said spring clip means holding said resistance element in placeand establishing electrical termination for said resistance element,said spring clip means each including a terminal portion extendingthrough said openings to the exterior of said variable resistors; ashaft positioned within said terminal cavity; and contact means carriedby said shaft so as to engage said resistance element, said contactmeans being movable along said resistance element.

5. A variable resistor as defined in claim 4 including ratchet likeprotruding extensions formed on each of said terminal portions, saidextensions engaging the exterior of said -base member so as to firmlyhold said clip means in position.

6. In a variable resistor having a housing, a leadscrew journaled onsaid housing, a resistance element mounted on said housing parallel tosaid leadscrew, a slider oper- -atively engaged by said leadscrew andmovable thereby lengthwise of the leadscrew, said slider having contactmeans wiping on said resistance element, a retainer mounted on saidhousing transverse to said leadscrew, said retainer comprising a bowedcli-p of spring metal having a U-shaped notch formed in one of thetransverse edges thereof adjacent the midpoint of the clip, the ends ofsaid clip bearing against said housing, and annular shoulder means onsaid leadscrew engaging said clip around the margin of said U-shapednotch, said clip resiliently urging said leadscrew in one direction soas to take up endwise clearance between said leadscrew and said housing.

7. The invention as defined in claim 6, wherein said leadscrew isprovided with a circumferential groove adjacent one end thereof, andsaid U-shaped notch of said retainer clip is engaged in saidcircumferential groove.

8. A variable resistor comprising an elongated housing having alengthwise extending cavity formed therein, a leadscrew journaled insaid housing and extending through said cavity, a resistance elementmounted within said cavity parallel to said leadscrew, a slideroperatively engaged by said leadscrew and having a contact wiping onsaid resistance element, a second cavity in said housing adjacent oneend thereof and separated from said first-named cavity by a partition,said partition having hole provided therein through which one end ofsaid leadscrew projects, said projecting one end of said leadscrewhaving a circumferential groove formed therein within said secondcavity, and a spring clip retainer seated Within said second cavity,said retainer having a U-shaped notch engaging said circumferentialgroove, and the ends of said retainer bearing against said partition,whereby said spring clip retainer resiliently urges said leadscrew inone direction.

References Cited in the file of this patent UNITED STATES PATENTS2,886,681 Bourns etal. May 12, 1959 UNITED STATES PATENT OFFICECERTIFICATION OF CORRECTION Patent No. 2,953763 im September 20XY 1960Marian E1 Bourns et al.- It is hereby certified that error appears inthe above numbered pat ent requiring correction and that the saidLetters Patent should read as corrected below.

Column 5, line 4L?Xl for "position" read M positioned Signed and sealedthis 15th day of August 1961i1 (SEAL) Attest:

ERNEST W. Svc/IDEE' DAVID-L. LADD Attesting Officer Commissioner ofPatents UNITED STATES PATENT OFFICE CERTIFICATION OF CORRECTION PatentNm. 2,95S763 September 2O,I 196.0v

Marian E@ Bourne et al.

It is hereby certified that error' appears in the above numbered patentrequiring coiection and that the said Letter-s Patent should read ascorrected below'.

Column 5, line I?u for "position" read positioned o Signed and Sealedthis 15th day of August l96l (SEAL) Attest:

ERNEST W. SWIDEEl DAVID'L. LADD Attesting Officer Commissioner ofPatents

